The experiments I propose are designed to investigate the DNA substrates involved in genomic rearrangement in animal cells. I intend to construct DNA molecules that are potentially recombinagenic, and to introduce these molecules into cultured cells. Such DNA molecules will be designed to reveal recombination by changing the phenotype of the cell. The ultimate aim of this approach is to construct cell lines that harbor ectopic DNA sequences that can be monitored for recombination by the application of growth conditions selective for the expression of recombinant genes. Use of such "recombination-indicator" cell lines will allow quantitation of recombination events in chromosomal DNA of mammalian cells. The primary application of recombination-indicator cells will be to study the effects of biological and chemical elements that appear to induce or mediate chromosomal rearrangements. The specific factors I propose to consider are the SV40 replicon and the recombinagenic drug, mitomycin C. A second aspect of DNA metabolism I propose to study is the cis-effects of simple-sequence DNAs that can readily assume a Z-DNA configuration. To this end, I will introduce tracts of alternating GT sequence into nonessential regions of the SV40 genome, and determine the effect of such sequences on recombination between viral and cellular DNA. In conjunction with this study, I will investigate the abundance and distribution of GT repeats in the mammalian genome via DNA hybridization and cloning.